1. Field of the Invention
This invention relates to a method and an apparatus for generating electric power by wave force of water.
2. Description of the Prior Art
The inventors of this application had completed an invention of wave power generation and filed it in Japan (Japanese Patent Application No. 26,725/80, Japanese Laid-open Patent Application No. 56-124,680). Thereafter, the inventors had improved and developed the filed invention to file it (Japanese Patent Application No. 22,883/81, Japanese Laid-open Patent Application No. 57-137,655) which provides a method and an apparatus for generating power by wave force with low construction and maintenance cost for effectively generating electric power and synchronously inputting the generated power into the public electric power system. This invention has been further improved and developed by the inventors to complete the invention of the present application.
The invention disclosed in the Japanese Laid-open Patent Application No. 57-137,655 comprises a series of caissons 1 each including a bottom plate 5, a back plate 4 and sidewalls 2 and 3, opening on an opposite side of the back plate and all or part of the upper portion of the caisson as shown in FIGS. 1 and 2. The plurality of the caissons 1 are arranged side by side adjacent to each other to form all or part of a breakwater or bank at a seashore with their open ends facing to the sea. A length Bc of a water chamber in the caisson 1 is substantially equal to one fourth of wave length Lc in the water chamber to produce stationary wave surges in the water chamber, whose wave forms have points of inflection at the location one fourth of the length Lc from the back plate on the side of the sea. The point of inflection means that where the wave form changes from under to above an average water surface or vice versa. A length of the caisson is of course larger than one fourth of the wave length Lc. A pendulum 7 having a natural period Tp in rocking or oscillating, which is substantially the same as a period Tw of the stationary wave surges, is located at the point of inflection. In this manner, the pendulum 7 is rocked or oscillated by the stationary wave surges so as to transmit the rocking movement of the pendulum to hydraulic motors or cylinders 10 which deliver the hydraulic liquid to drive a hydraulic motor 21 which in turn drives a generator 23 at a constant speed (FIG. 2).
Referring to FIG. 2, each the hydraulic cylinder 10 is supplied with the hydraulic liquid from a reservoir 11 through a line 12, flow rectifier valve means 13 and lines 14 and 15. When the pendulum 7 is rocked or oscillated by the wave force, the hydraulic liquid supplied into the left and right sides of a piston 10a of the each hydraulic cylinder 10 is alternately introduced into the hydraulic motor 21 through a line 16, a reducing valve 20 and a line 26 including an accumulator 25. A flywheel 22 is interposed between the hydraulic motor 21 and the generator 23. A relief valve 24 is provided between the line 16 and a returning line 19 connecting the hydraulic motor 21 to the reservoir 11.
With this arrangement, all the components which require maintenance such as bearings 9 are not in the water, and the entire system is very simple in construction and is connected to the public electric power network to operate with high efficiency.
An energy L per unit time of the hydraulic liquid delivered from the hydraulic cylinders 10 is indicated by a product of hydraulic pressure P and delivered flow rate Q as follows. EQU L=PQ (1)
When the pendulum 7 rocks or oscillates according to a sine wave and the hydraulic pressure P is controlled so as to be in proportion to the rocking velocity .vertline..theta..vertline. of the pendulum 7, the energy L is indicated as in the following equation: EQU P=Kp.vertline..theta..vertline. (2)
because EQU Q=Kc.vertline..theta..vertline. (3)
hence EQU L=KpKc.theta..sup.2 ( 4)
where Kp and Kc are proportional constants, respectively. In other words, if .theta.=.theta..sub.o sin .omega.t, the energy L is again indicated in the following other equation, where .theta. is an rocking angle of the pendulum 7, the maximum rocking angle .theta..sub.o, an angular velocity .omega. of the rocking movement and time t. EQU .theta.=.theta..sub.o .omega. cos .omega.t (5)
hence EQU L=KpKc(.theta..sub.o .omega.).sup.2 cos.sup.2 .omega.t (6)
From the equation (6), it is evident that the energy L periodically changes (refer to characteristic of generated output in FIG. 3). It may cause undesirable phenomena such as the electric voltage fluctuation or the like, if the output is directly connected to the public power network.